Golf ball manufacturers generally are interested in determining a golf ball's trajectory, which predicts the ball flight distance. Typically, a golf ball's drag and lift coefficients are used to predict the trajectory of the golf ball. Manufacturers have used three techniques for determining a golf ball's drag and lift coefficients. Two conventional techniques use a wind tunnel and the remaining technique uses an indoor testing range.
The first technique uses a golf ball that is supported on a spindle within the wind tunnel. The spindle is affixed to the surface of the ball. The spindle freely rotates on low friction bearings. With the ball immersed in the wind stream, a motor coupled to the spindle spins the ball up to a predetermined spin rate and speed. The motor is disconnected from the spindle, and the ball continues to spin under the influence of its inertia and spin decay rate. The ball's lift and drag are monitored as the ball spins to a stop. The lift and drag are used to determine the trajectory.
This method is problematic for several reasons. First, there is a turbulence level present in the airstream of any wind tunnel, which is not present in the atmosphere through which a golf ball normally flies. Since a golf ball's aerodynamics are fundamentally turbulence driven, this can significantly affect the outcome of the test.
Second, in the wind tunnel the wind stream around the ball is disturbed at the point where the spindle is joined to the ball. This affects the measurements in a way for which it is difficult to compensate.
The second technique also uses the wind tunnel. A ball is spun up to speed outside the tunnel, then dropped into flowing air in the tunnel. The trajectory of the ball is then measured. The problems associated with using a wind tunnel, discussed above also occur using this method. In the second technique, the trajectory needs to be recorded in considerable detail, and the results are probably not highly accurate.
The third technique uses a series of ballistic light screens, where the screens alternate between being vertical or inclined. U.S. Pat. No. 5,682,230 to Anfinsen et al. discloses such an arrangement. When using this set-up, the ball is launched into flight and passes through the series of screens. The orientation of the screens allows the velocity and ball's coordinates to be measured. This information is used to determine the ball's trajectory.
This method is troublesome, because the test set-up requires determining the precise location of each light screen. Locating each light screen involves firing numerous balls. This is undesirable because it is time consuming.
It would therefore be desirable to provide an improved method for determining the drag and lift coordinates of a golf ball, while the ball is in actual flight.